Forging apparatus and control thereof



Oct. 28, 1952 R. L. ALCJ ORN, JR

FORGING APPARATUS AND CONTROL. THEREOF 5 Sheets-Sheet 1 Filed July 21, 1949 Oct. 28, 1952 R. L. ALCORN, JR

FORGING APPARATUS AND CONTROL THEREOF 5 sheetsw-s'neet 2 Filed July 21, 1949 Had.

Oct. 28, 1952 R. L. ALCORN, JR 2,615,306

FORGING APPARATUS AND CONTROL THEREOF Filed July 21, 1949 5 Sheets-Sheet s 55 five/2707"."

Oct. 28, 1952 R. ALCORN, JR 2,615,305

FORGING APPARATUS AND CONTROL THEREOF Filed July 21, 1949 5 Sheets-Sheet 4 Oct. 28, 1952 R. 1.. A-LcoRN, JR

FORGING APPARATUS AND CONTROL THEREOF Filed July 21, 1949 5 Sheets-Sheet 5 Patented Oct. 28, 1952 FORGING APPARATUS AND CONTROL THEREOF Robert L. Alcorn, J r., Chambersburg, Pa., assignor Chambersburg Engineering Company,

Chambersburg, Pa., a corporation of Pennsylvania Application July 21, 1949, Serial No. 106,045

16 Claims.

This invention relates to forging apparatus and the control thereof, and more particularly to the control of an apparatus of the type wherein two horizontally aligned rams, operated by pressurized fluid, serve to forge by impact work pieces interposed between them.

The principal object of the invention is to provide an improved apparatus for accurately controlling the forging operation.

In an apparatus of this character, precise timing of the forging blow is very important. It is necessary to apply pressurized fluid to the rams during a very short time interval which may be a small fraction of a second. Moreover, it is highly desirable to provide for rapid successive operation of the apparatus in order that work pieces may be forged in rapid succession.

A further object of the present invention is to provide an apparatus which enables such precise timing and rapid cyclic operation. The apparatus is novelly characterized in that it comprises a cycling mechanism and an electronic timer under control of said mechanism.

It is also desirable in such an apparatus to be able to control with greataccuracy the intensity of the forging blow, and it is a further object of this invention to provide such control. This is achieved by means of the electronic timer which is adjustable to control the intensity of the forging blow.

Still another object of the invention is to provide means for differentially controlling the supply of pressurized fluid to the rams to establish the exact plane of impact of the rams.

A further object of the invention is to provide means for preventing or interrupting a forging operation in the event that a dangerous unbal- 'ance of pressure should develop.

Other objects and features of the invention will be apparent hereinafter.

The invention may be fully understood from the following detailed description with reference to the accompanying drawings, wherein Fig. l is a view, partly in longitudinal section and partly in elevation, of a forging apparatus embodying the present invention;

Fig. 2 is an end elevational view taken along line 22 of Fig. 1, with a portion of the apparatus broken away for the sake of illustration;

Fig. 3 is a sectional view taken along line 3--3 of Fig. 1;

Fig. 4 is a sectional view taken along line 4-4 of Fig. 2;

Fig. 5 is a schematic illustration of the controlling arrangement employed in conjunction with the impacter rains;

Fig. 6 is a diagrammatic illustration of the electrical system which serves to control the operation; and

Fig. '7 is a diagrammatic illustration of the electronic timer which is employed in the electrical system.

Referring first to Fig. 1, there are shown two horizontally aligned rams l0 and Illa which are movable within fluid cylinders II and Ha, the rams moving toward and away from each other during a complete cycle of operation. Removably attached to the rams are dies 12 and 12a which engage a work piece (not shown) to forge the same.

The rams are actuated during the work stroke by pressurized fluid supplied to the cylinders from a common fluid line l5 through intake conduits l6 and Wu. Preferably, the rams are actuated by means of compressed air, the line It being connected to a suitable source of compressed air. The air is supplied to the cylinders through manually-adjustable valves IT and Ila having adjustable levers l8 and l8a which may be set in any desired position.

As shown in Fig. 1, the ram-containing cylinders are mounted on a supporting framework l9 which may also serve to support certain controlling valves as hereinafter described. The supply conduit l5 extends longitudinally through the supporting framework, as does also a common exhaust conduit 20 (see Fig. 2) through which the air is exhausted from the cylinders during the return stroke.

Referring still to Fig. l, provision is made for supplying pressurized fluid through n axial passage in each ram to the associated die, the purpose of which is to cool the die block and to facilitate removal of the forged work pieces and also to facilitate scale removal. Since both rams are alike, only the left-hand ram in Fig. l is illustrated in detail. An axial passage 2! is provided in the ram, and the pressure end of the ram has a recess 22 to accommodate a fluid sup ply conduit 23. The conduit 23 is attached firmly to the ram by a tapered lit in recess 22 and reciprocates with ram [0 through packing gland 25 which allows the introduction of fluid through passage 2| without danger of mixing with the main operating fluid. The passage 2| communicates with passages l3 in the die block.

As also shown in Fig. 1, a pressure-responsive device 26 is connected by means of conduits 21 and 21a to the pressure ends of the respective cylinders. The device 26 quickly responds to a difference in pressure between the cylinders and, as hereinafter described, it serves to interrupt the operation in the event that a pressure unbalance develops in excess of a safe maximum.

Referring now to Figs. 2 to 4, these figures illustrate the controlling valves associated with the ram I and its cylinder II, it being understood that similar valves are provided in association with the ram a and its cylinder I Ia. A fluid-operable valve 28 controls the air input from conduit I6 to the ports 29 which extend to the interior of the cylinder at the pressure end thereof. A second fluid-operable valve 30 controls the air exhaust to conduit 3I which extends to the exhaust line 29. The valves 28 and 30 are arranged in a common valve casing designated generally by reference character 32 which also contains the manually-operable valve H. In the illustration of Fig. 3, the valve 28 is closed and the valve 39 is open, this being the condition for exhaust. When the valve 30 is closed and the valve 28 is open, air is admitted to the cylinder from conduit I5 at a rate dependent upon the setting of valve H.

In order to positively prevent mixture of the valve operating fluid and the main operating fluid, a passage 30a is provided which serves to by-pass leakage of either fluid to the exhaust conduit 3]. The passage 30a extends to an annular recess 23a and holes 28b in the guide around valve 28.

As may be seen in Fig. 3, the ports 29 are in communication with the valve ports 33 and 34 through a common chamber or space 35. As shown in Fig. 4, the ports 29 are spaced from the cylinder head 24, and a by-pass port 36 is disposed immediately adjacent the cylinder head 24 and is adapted to be placed in communication with a transverse port 3'! leading to the chamber or space 35. A spring-biased check valve 38 normally closes the port 31 under the influence of its spring 39. This valve is supported by a plug 40 bolted to the valve casing. The purpose of the check valve and the by-pass controlled thereby will be explained presently.

Referring generally to Figs. 1 to 5, and particularly to the schematic illustration of Fig. 5,

the inlet valve 28 for the ram I0 and its associated cylinder II is controlled by pressurized fluid, preferably compressed air, through a conduit 4I extending to casing 42 of a differential controlling valve 43. In like manner, the input valve for the other ram and its associated cylinder is controlled through the fluid conduit 44 which extends from said valve to the other side of the controlling valve 43. The conduits M and 44 communicate, through valve casing 42, with a common fluid conduit 45 which extends from the valve casing 42 to the casing 46 of a valve 47. The purpose of the differential controlling valve 43 is to control differentially the supply of fluid to the input valves for the two rams, thereby to control the relative timing of the operation of the input valves and thus establish the exact plane of impact of the rams. The valve 43 has a crank arm 48 which is connected through link 49 to a crank arm 59 on a shaft 5I. This shaft is connected through reducing gears 52 and. 53 to the shaft 54 of a Selsyn receiver 55. The purpose of this is to provide for remote control of the valve 43 as hereinafter described.

The exhaust valve 30 for the ram I0 and its associated cylinder II is controlled through branch 56 of a T conduit 57. The other branch arm 58 of the T conduit extends to the exhaust valve for the other ram and its associated cyl- 4 inder. The leg of conduit 51 extends to the casing 46 of the valve 41.

The valve 4'! is spring biased to the position shown by means of spring 59, and it is actuated against the action of the spring by a solenoid 60. The casing of this valve has spaced annular recesses BI and 82 to which are respectively connected the conduits 45 and 51. Between these annular recesses is an annular recess 63 to which a compressed air conduit 64 extends. This conduit may be connected to the main air supply conduit I5 hereinbefore mentioned. Exhaust conduits 65 and 66 extends into the ends of valve casing 46, and these conduits may be connected to the main exhaust line 20 hereinbefore mentioned. The valve member 41 has spaced portions 6'! and 68 which control the valve ports.

When the solenoid 60 is deenergized as shown, the input valve 28 is in communication with the air supply conduit 64 and the valve is held closed. At the same time, the exhaust valve 30 is in communication with exhaust conduit 66 and that valve is open. When the solenoid 60 is energized, the valve member 47 moves to the right, and the exhaust valve 30 is placed in communication With the air supply conduit 64 and is cut off from the exhaust conduits. At the same time, the input valve 28 is cut oif from the air supply conduit 64 and is placed in communication with the exhaust conduit 65. At such time, therefore, the exhaust valve 30 is closed and the input valve 28 is opened.

After the impacting stroke of ram II], the ram is returned by air pressure supplied to the cylinder II through branch 69 of a T conduit I0 whose other branch arm 'II extends to the cylinder of the other ram. The leg of the T conduit 59 extends to the casing 12 of a valve I3 which is biased by spring 14 and is operable by a solenoid I5. An air supply conduit 16 and an exhaust conduit I'I also extend to the valve casing I2. These conduits may be connected respectively to the main air line I5 and the main exhaust line 20 hereinbefore mentioned. Normally, the valve I3 is in the position shown, and the conduit I0 is in communication with the exhaust conduit 11. However, when solenoid I5 is energized, the conduit I0 is placed in communication with the air conduit I8 and is cut off from the exhaust conduit I1. At such time, air is supplied to the cylinder I I to move the ram I0 back to its initial position.

From the description thus far, it will be seen that the operation of the rams is controlled by means of the solenoids 60 and I5. These solenoids are controlled by the electrical control system presently to be described.

The purpose of the check valve 38 may now be understood. Referring still to Fig. 5, the disposition of the ports 29, with reference to the end of the cylinder II, provides an air cushioning action when the ram I0 is returned. During the return of the ram, the head thereof closes the ports 29 and air is trapped at the end of the cylinder, providing an air cushion which prevents the ram from striking the cylinder head. This becomes particularly important if the ram should rebound due to the impact.

With the ram stopped in the position shown in Fig. 5, the cylinder is closed against intake of air through the ports 29. However, the check valve 38 and the by-pass 3B permits air to enter the cylinder from the chamber or space 35, and such air moves the ram until the ports 29 are cleared. It should be noted that the check valve does not interfere with the above-mentioned air cushioning action, since it will not permit air to leave the cylinder by way of the by-pass.

Mention was made above of the unbalanced pressure-responsive device 26, and it may now be noted from Fig. 5 that this device comprises a two-part casing 18 containing a pressure-responsive diaphragm 19 which is subject to the air pressure transmitted through conduits 21 and 21a. The casing carries contacts 80 and 8I whose inner ends are in spaced relation to one another, and the diaphragm carries a contact 82 which is normally out of engagement with. the stationary contacts but may engage either of those contacts when there is sufficient unbalance of the pressures in conduits 21 and 21a. The diaphragm 19 is formed of conductive ma terial and it is provided with a terminal 83. The casing parts are formed of insulating material. The screw contacts 80 and 8| and the terminal 83 are connected to the electrical system as hereinafter described.

Referring now to Fig. 6, an A. 0. supply line 84, 85, e. g. a 60 cycle supply line, serves as a common source of electrical supply for the various elements through the manual switch 86. It will be recalled that the diiferential control valve 43, shown in Fig. 5, is actuated by a Selsyn receiver 55. Fig. 6 shows the complete Selsyn system for actuating the valve 43, which system is of conventional form and comprises the receiver 55 and a transmitter 81 connected to each other and to the line conductors 84 and 85. Thus the valve 43 is remotely controllable from the Selsyn transmitter 81.

It will also be recalled that the operation of the rams is controlled by means of the solenoids 60 and 15. The energization of solenoid 80 is effected by means of a timer 88 under control of a motor-driven switch mechanism 89. The energization of solenoid is effected by the switch mechanism 89. The manner in which the two solenoids are controlled will be described presently.

The electrical control system is conditioned for operation, after closure of switch 88, by a contactor 90 which is under control of-start and stop switches 9I and 92. The contactor 90 comprises a solenoid 93, an armature 94, and a biasing spring 85 which tends to maintain the armature in the position shown. When the start switch 9I is momentarily closed, the solenoid 93 is energized through a circuit which includes conductor 96, conductor 91, the closed contacts of a safety device 98, conductor 99 and conductor I00. The contactor locks itself in through contacts IOI which close a branch circuit in shunt with the start switch 9| and including conductors I02 and I03.

Energization of the contactor closes an energizing circuit for the motor I04 of the device 89 through closure of contacts I05 and I06. This circuit includes conductors I01, I08, I09, and H0. The motor I04 drives, through reduction gearing I04a, a shaft III on which are '6 switch H4, and back to the timer by 'way of conductor I2I. A number of safety switches I22 are shown serially included in the initiating circuit, to which reference will be made later. Switch II5 of device 89 is included in an en'- ergizing circuit for solenoid 15, which circuit is in shunt with the solenoid 93 of contactor 90.

The impulse timer 88 has energy input terminals I23 and I23a which are connected to supply line 84, via conductors I24. 'A lamp I25 is connected across the latter conductors to indicate closure of switch 86. This lamp preferably gives off green light. A second lamp I28, which preferably gives off red light, is connected to terminals I21 of the timer, this lamp indicating that the timer is conditioned for operation. Start and stop switches I28 and I29 are connected to terminals I30, I3I and I32 of the timer in the manner shown and serve to control the conditioning of the timer for operation as hereinafter described.

The pressure-responsive device 26, hereinbefore described, is connected to terminals I33, I34 and I35 of the impuse timer.

The impact-controlling solenoid 60 is connected between terminal I38 on the impulse timer and one of the supply line conductors through connections I31 and I38.

The impulse timer 88 functions to supply an impulse of accurately timed short duration to the solenoid 60. While this timer may be of any suitable type, a preferred form thereof is shown in Fig. 7. The impulse timer shown is a modified Westinghouse type SP-19 timer which provides a precisely timed output impulse. So far as its general structure and operation are concerned, this timer is a known device and it need only be described here sufficiently to enable a complete understanding of the present invention.

As may be seen in Fig. 'I, the timer comprises a start tube I39, a stop tube I40, a bias-providing tube I4! and a pair of controlled power tubes I42 and I43. All of the tubes are thyratrons with the exception of tube I4I which is a double diode rectifier. The tubes I42 and I43 constitute a lead and follow combination, tube I42 being the lead tube and tube I43 being the follow tube. Condenser I44 is a timing condenser, the charging of which determines the time duration of the output impulse.

Relays I41 and I48 are provided to control the timer as hereinafter described. These relays and the several transformers shown with their primary windings unconnected are energized from the power supply line by way of terminals I23 and I23a. The connections are omitted for simplicity of illustration.

In the inoperative state of the timer, all of the thyratrons are non-conducting due tothe potentials applied to their control grids. The condenser I44 is fully discharged through a resistor I45 which is connected across the condenser through normally closed contacts I46 of a relay I41.

As hereinbefore mentioned, the timer is conditioned for operation by closing the start switch I28 which energizes relay I48. This relay locks itself in through contacts I49. Its contacts I50 are included in the output circuit of the timer, but the solenoid 60 remains deenergized because of the non-conductive condition of the tubes I42 and I43. The lamp I26 indicates that the relay I48 has been energized and that the timer is in condition for operation.

When the initiating circuit II6 (see Fig. 6) is closed by closure of switch I14, relay I4! is energized. This relay opens the discharge circuit for condenser I44, and its contacts I close and cause a variation of the potential on the control grid of tube I39, thus causing that tube to fire. Conduction of tube I39 initiates charging of con denser I44 through one side of the rectifier tube MI, and it also causes tube I42 to fire. The latter in turn furnishes a firing impulse for tube I43. When tubes I42 and I43 become conductive, the output circuit is closed and furnishes current to the solenoid 68. In the meantime, tube I49 has remained non-conductive by virtue of the D. C. bias on its control grid.

When the voltage on condenser I44 rises to a value approximately equal to the D. C. bias on tube I40, this tube fires and renders tubes I42 and I43 non-conductive. At this time, the solenoid 60 is deenergized. When the switch II4 opens, relay I4! is deenergized and the timer is restored to its inoperative condition and is ready for the next operation when switch I I4 closes.

The charging rate of condenser I44 is controllable by means of potentiometer I52. Since the rate of charge of the condenser determines the time during which operating fluid is supplied to the rams, the adjustment of the potentiometer I52 sets the intensity of the forging blow With great accuracy.

A second potentiometer I 53 constitutes a power factor adjustment, the purpose of which will be described later.

It should now be noted that the pressure unbalance responsive device 26 will interrupt the operation of the timer if contact is made in said device due to an undesirable unbalance of the pressures in the ram cylinders. Upon such contact being made, the grid of tube I42 is driven to a potential considerably negative with respect to its cathode, and current flow to the solenoid 60 is cut off in less than the time of one cycle of the A. C. supply current. This prevents the completion of the forging blow in the event that seriously unbalanced pressures are driving the rams.

Considering the operation of the apparatus as a whole, and referring particularly to Fig. 6, the operator first closes the line switch 8-3 and then presses the push button start switch 9|, whereupon the contactor 9G is energized and locks itself in as hereinbefore described. The contactor 90 remains energized until such time as the operator presses the push button stop switch 92 which is connected in the holding circuit of contactor 90. The energization of contactor 96 starts the motor I04 which runs continuously until the contactor is deenergized. Consequently, the switches II 4' and H5 are cyclically operated by their motor driven cams II2 and H3. The cam H2 is so designed that the switch I I4 is held closed during a time interval within which the timer 88 may effect timed energization of the solenoid 6!] as hereinbefore described. The cam H3 is so designed that it closes switch I I5 after switch I I4 has opened.

With the apparatus conditioned for operation by energization of contactor 90, the operator may start the operation at any time by pushing the push button start switch I28 for the timer 88. This causes energization of relay I48 (see Fig. 7) which looks itself in. The timer will then operate cyclically under control of switch H4 until such time as the operator pushes the push button stop switch 29.

During each cycle of operation, the switch H4 starts the timer 88 and the latter effects energization of solenoid 60 during an accurately timed interval, as hereinbefore described. The energization of solenoid 50 causes operation of the rams through their work stroke to forge the work piece by impact. After the timed energization of solenoid 69, the solenoid I5 is energized by closure of switch I I5, and the rams are returned preparatory to the next work stroke. This cycle of operation is repeated automatically until such time as the operator presses the push button stop switches I29 and 32. In the illustrated embodiment, a cycle of operation takes place during onehalf revolution of the shaft HI, and the cams are designed accordingly.

It will be apparent that the work pieces must be fed to the impacter apparatus and this may be done automatically by the provision of suitable automatic feeding means. Since the present invention is not concerned with the feed mecha nism, it suffices to note that such mechanism could be pneumatically operated and could be controlled by a valve I54 (see Fig. 6) operable by a solenoid I55 under control of a switch I 55 which may be cyclically operated by a cam I51 on the motor driven shaft of the switch mechanism 89.

The cycling switch mechanism 89 may also be used to control other functions. For example, a valve I58, operated by solenoid I59, may control the air supply to the axial passages of the rams, and the solenoid may be controlled by a switch I68 and. an actuating cam I5I on the switch mechanism 89.

Referring still to Fig. 6, mention was made above of the safety device 95 and the safety switches I22. These are desirable optional devices. The device 98 prevents or interrupts energization of contactor in the event that the pressure of the operating fluid rises above a predetermined maximum or falls below a predetermined minimum. This device may comprise two switches as indicated arranged for response to pressure of the fluid. The safety switches I22 may be controlled by various conditions so as to prevent operation of the timer 83 in the event that some undesired condition exists. For example, one of these switches may be arranged so as to be closed only if the work pieces are properly positioned. Another of these switches may be responsive to temperature produced b the means for heating the work pieces prior to forging. Still another of these switches may be arranged so as to open if certain guards for the operators safety are removed. As many of these switches may be provided as are necessary to assure proper and safe operation.

The complete apparatus and its operation having now been described, it is deemed desirable to recapitulate and emphasize the salient features and advantages.

The predominant feature of the apparatus is the control of the forging operation by the doctronic timer and the cyclic operation of the timer by the cyclin switch mechanism. Such control of the forging operation provides a number of important advantages as set forth below.

The electronic timer provides an extremely short timing interval which may be as short as the time required for two cycles of the Gil-cycle current. Furthermore, the electronic timer makes it possible to adjust the occurrence of the timing interval according to the natural power factor of the solenoid 60. Due to the inductive nature of the solenoid, the duration of its energization is affected by the point on the voltage'wave at which the circuit is made and broken with respect to the current. It will be understood, of course, that the voltage and current waves do not coincide but are displaced according to the power factor of the solenoid. The potentiometer I53 (Fig. 7) enables adjustment of lag of the application of voltage to suit the power factor of the solenoid.

A further advantage of the system is that the intensity of the forging blow can be set with great accuracy by adjustment of potentiometer I52. A light blow may be struck by setting the potentiometer so that the charging of condenser I44 occupies the time of three cycles; or a heavy blow may be struck by a setting such that the charging of the condenser occupies the time of eight cycles. This enables pre-selection of the blow Without disturbing the air supply pressure.

A further advantage of the system is that the operation of the timer is interrupted by unbalanced pressures through the medium of the pressure responsive device 26.

Another feature of the apparatus is the differential control of the input valves for the rams to establish the exact plane of impact.

It will be apparent from the foregoing description that the invention provides a novel apparatus which embodies various desirable features and which has important advantages. particular embodiment of the apparatus has been illustrated and described, it is to be understood that the invention is not limited thereto but is capable of various modifications and further embodiments.

I claim:

1. In an apparatus of the class described, fluidoperated means, means for supplying pressurized fluid to said first means, means including a valve for controlling thesupply of fluid to said first means, a solenoid for actuating said valve, a source of electric current, cyclically-operable timing means for supplying current from said source to said solenoid during an accurately timed interval, and power-driven cycling switch means for controlling the operation of said timing means. I

2. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, means r for supplying pressurized fluid to said cylinders so as to drive said pistons toward each other, means including a valve for controlling the supply of fluid to said cylinders, a solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said cylinders so as to return said pistons, a second solenoid for actuating said second valve, energizing circuits for said solenoids, cyclically-' operable timing means for effecting energization of said first solenoid during anaccurately timed interval, and power-driven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid.

3. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, input and exhaust valves operatively connected to one end of each cylinder, fluid supply and exhaust means under control of said valves, means including a solenoid for actuating said valves, means including another valve and an operatingsolenoid therefor for supplying pressurized fluid to said cylinders at the other end thereof so as to While a return the pistons, energizing circuits for said solenoids, cyclically-operable timing means for effecting energization of said first solenoid during an accurately timed interval, and powerdriven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid.

4. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, means for supplying pressurized fluid to said cylinders so as to drive said pistons toward each other, means including a valve for controlling the supply of fluid to said cylinders, a solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said cylinders so as to return said pistons, a second solenoid for actuating said second valve, energizing circuits for said solenoids, cyclically-operable timing means for effecting energization of said first solenoid during an accurately timed interval, means for adjusting said timing means to set precisely the desired timed interval, and power-driven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid.

5. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, input and exhaust valves operatively connected to one end of each cylinder, fluid supply and exhaust means under control of said valves, means including a solenoid for actuating said valves, means including another valve and an operating solenoid therefor for suppling pressurized fluid to said cylinders at the other end thereof so as to return the pistons, energizing circuits for said solenoids, cyclically-operable timing means for effecting energization of said first solenoid during an accurately timed interval, means for adjusting said timing means to set precisely the desired timed interval, and power-driven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid.

6, In an apparatus of the class described, a pair of fluid cylinders, means for supplying pressurized fluid to said cylinders, means for detecting an unbalanced pressure rise in said cylinders, and means responsive to detection of such condition for interrupting the supply of fiuid to said cylinders.

'7. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, means for supplying pressurized fiuid to said cylinders, means for detecting an unbalanced pressure rise in said cylinders, and means responsive to detection of such condition for interrupting the supply of fluid to said cylinders.

8. In an apparatus of the class described, a pair of opposed pistons, a pair of fluid cylinders for the respective pistons, means for supplying pressurized fluid to said cylinders, means including a valve for controlling the supply of fluid to said cylinders, a solenoid for actuating said valve, a source of electric current, timing means for supplying current from said source to said solenoid during an accurately timed interval,-

and means responsive to an unbalanced pressure rise in said cylinders for interrupting the operation of said timing means so'as to interrupt the fluid cylinders for the respective pistons, means for supplying pressurized fluid to said cylinders so as to drive said pistons toward each other, means including a valve for controlling the supply of fluid to said cylinders, a solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said cylinders so as to return said piston, a second solenoid for actuating said second valve, energizing circuits for said solenoids, cyclically-operable timing means for effecting energization of said first solenoid during an accurately timed interval, powerdriven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid, and means responsive to an unbalanced pressure rise in said cylinders for interrupting theoperation of said timing means so as to interrupt the energization of said first solenoid.

10. In an apparatus of the class described, a pair of horizontally opposed pistons, a pair of fluid cylinders for the respective pistons, input and exhaust valves operatively connected to each cylinder, fluid supply and exhaust means under control of said valves, means including a solenoid for actuating said valves, means including another valve and an operating solenoid therefor for supplying pressurized fluid to said cylinders so as to return the pistons, energizing circuits for said solenoids, cyclically operable timing means for effecting energization of said first solenoid during an accurately timed interval, power-driven cycling switch means for initiating operation of said timing means and for controlling the energization of said second solenoid, and means responsive to an unbalanced pressure rise in said cylinders for interrupting the operation of said timing means so as to interrupt the energization of said first solenoid.

11. In combination, fluid pressure-actuated mean operable through a work stroke and a return stroke, means for supplying pressurized fluid to said first-mentioned means so as to operate the same through the work stroke, means including a first valve for controlling the supply of fluid to said first-mentioned means, a first solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said first-mentioned means so as to operate the same through the return stroke, a second solenoid for actuating said second valve, a pair of cyclically-operable switches, actuating means for said switches, cyclically-operable timing means under control of one of said switches and adapted to operate through a timing cycle each time the switch closes, an energizing circuit for said first solenoid controlled by said timing means, and an energizing circuit for said second solenoid controlled by the other of said switches.

12. In combination, fluid pressure-actuated means operable through a work stroke and a return stroke, means for supplying pressurized fluid to said first-mentioned means so as to operate the same through the work stroke, means including a first valve for controlling the supply of fluid to said first-mentioned means, a first solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said first-mentioned means so as to operate the same through the return stroke, a second solenoid for actuating said second valve, a pair of camactuated cyclically-operable switches, an electric motor arranged to drive the actuating cams of said switches, cyclically-operable timing means under control of one of said switches and adapted to operate through a timing cycle each time the switch closes, an energizing circuit for said first solenoid controlled by said timing means, and an energizing circuit for said second solenoid controlled by the other of said switches.

13. In an apparatus of the class described, a pair of opposed pistons, a pair of fluid cylinders for the respective pistons, means for supplying pressurized fluid to said cylinders so as to drive said pistons toward each other, means including a first valve for controlling the supply of fluid to said cylinders, a first solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said cylinders so as to return said pistons, a second solenoid for actuating said second valve, a pair of cyclically-operable switches, actuating means for said switches, cyclically-operable timing means under control of one of said switches and adapted to operate through a timing cycle each time the switch closes, an energizing circuit for said first solenoid controlled by said timing means, and an energizing circuit for said second solenoid controlled by the other of said switches.

14. In an apparatus of the class described, a pair of opposed pistons, a pair of fluid cylinders for the respective pistons, means for supplying pressurized fluid to said cylinders so as to drive said pistons toward each other, means including a first valve for controlling the supply of fluid to said cylinders, a first solenoid for actuating said valve, means including a second control valve for supplying pressurized fluid to said cylinders so as to return said pistons, a second solenoid for actuating said second valve, a pair of cam-actuated cyclically-operable switches, an electric motor arranged to drive the actuating cams of said switches, cyclically-operable timing means under control of one of said switches and adapted to operate through a timing cycle each time the switch closes, an energizing circuit for said first solenoid controlled by said timing means, and an energizing circuit for said second solenoid controlled by the other of said switches.

15. Apparatus according to claim 13, including means for differentially controlling the fluid supplied to said cylinders through said first valve.

16. Apparatus according to claim 13, including means for detecting an unbalanced pressure rise in said cylinders, and means responsive to detection of such condition for interrupting the supply of fluid to said cylinders.

ROBERT L. ALCORN, JR.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 232,792 Whitcomb Sept. 28, 1880 776,159 Whiteside Nov. 29, 1904 1,012,334 Davis Dec. 19, 1911 1,375,562 Cartzdafner Apr. 19, 1921 1,785,998 Brooke Dec. 23, 1930 1,985,589 Meer Dec. 25, 1934 1,999,834 Ernst Apr. 30, 1935 2,019,766 Peterson Nov. 5, 1935 2,354,860 Hartsock Aug. 1, 1944 2,443,964 Sanders June 22, 1948 2,467,576 Zimmermann Apr. 19, 1949 

